prime



UNTTEB STATES PATENT OFFICE.

JNO. PRIME, OF WASHINGTON, NORTH CAROLINA.

SHIPS COMPASS.

Specification of Letters Patent No. 14,251, dated February 12, 1856.A

To all whom t may concern:

Be it known that I, JOHN PRlME, of Nashingtom in the county of Beaufort and State of North Carolina, have invented a new and useful Improvement in Compasses; and I do hereby declare that the following is a full, clear, and exact description of the same, reference being had to the accompanying drawing, forming part of this specification, in which- Figure l, is a central sect-ion of a mariners compass, constructed according to my invention, and Fig. 2, an inverted plan or underside view of the compass card.

Similar letters of reference indicate corresponding parts in both figures.

The object of my improvement is to make the glass serve as or form a perfectly watertight covering to the compass bowl or box. In mariners Compasses of the ordinary kind, the glass is flat and fitted into a rabbet formed in the head of the bowl or boX, and a close joint is made by the application of putty to cover the edge of the glass. This is liable to the following objections: The frequent expansion and contraction of the bowl or boX by changes of atmospheric temperature soon cracks the putty and the glass being a little lower than the surrounding rim of the head, forms, as it were, a cup to receive rain, which soon works through the cracked putt-y into the bowl, and not only damages the card but rusts the needle and the point upon which the needle rests and when it is evaporated by the sun or the heat of the atmosphere, it dims the glass frequently to such an-eXtent as to completely obscure the card. In surveyors Compasses a metal ring is used in place of the putt-y to cover the edges of the glass, but this fails to shed rain and is liable t-o all the same disadvantages as the employment of putty.

To obviate this, my improvement consists in making the glass in the form of a cap with a rim to fit over the head of the bowl to shed off' all t-he water and in protecting the glass from being cracked by the eXpansion of the bowl, by means of a ring of elastic material placed between the head of the bowl and the rim of the glass cap.

To enable those skilled in the art to make and use my invention, I will proceed to describe its construction and operation.

A, is the bowl or boX and B, a metal ring forming part of the head of the said ring fitting over the top of the bowl. This ring is made with a slight recess in its outer surface. C, is the glass cap which is blown or otherwise formed with a rim to fit over the ring B, within the recess c. A ring a?, of india rubber, gutta percha, wool, cotton or cloth or any other elastic or yielding material is placed between the ring B, and cap C, to prevent the expansion of t-he said ring acting forcibly on the glass cap; and the lower edge of the ring is covered with putty. The top of the glass cap may be either flat or convex. It will be understood that rain or condensed moist-ure falling or settling on the glass cap C, cannot by any possibility so long as the compass remains upright, find its way into the bowl, but will be shed or run off.

D, is the compass card and E, is the needle, which are attached together and poised in the usual way upon a fine central point b, wit-hin the bowl. To the center socket' c, which is fitted to the point b, and supports the needle and card, are attached four arms c, e, e, c, standing at equal distances apart. These arms are screwed and provided each with a nut, f to serve as a balance weight, but they may be plain and be provided with sliding weights fitted with springs so as not to move too easily. By screwing or moving these weights to or from the center, as may be necessary, the card may be balanced accurately and the variable dip of the needle as it advances to or recedes from the magnetic equator, be at any time accurately compensated for.

What I claim as my invention and desire to secure by Letters Fatent is- The method herein described of constructing the cover of compass-boxes by inserting the metallic ring (B) within the rim of the glass with a band of india rubber or other elastic material between them to compensate for their unequal expansion and contraction ubsltlant-ially as and for the purposes set ort JOHN PRIME.

Witnesses: V

J. G. MASON, WM. TUscH. 

